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After a nice Single Ended with Russians 6P3C and 6N2P, I would like to start another tubes project, another amplifier, but this time with the Russians double tetrodes GU29, that I have a NOS pair. I like very much the shapes of this tetrode I want to know if somebody has made this kind of amplifier and I want to try a good and tested schematic, whatever if it is Single Ended or Push Pull, but simplest as possible, with schematic, of course, of power supply. I have a few schematics, but I'm not sure how reliable are.

Hi, I have not used the GU29s ,but did use the GU32s in a "oddwatt" circuit. At first I tried to use just one tube per channel in push-pull ultra linear class A mode. The common cathode made it impossible to balance the tubes in the same way as the other amps, so I used the variation similar to the Poddwatts with a CCS in the cathode circuit and variable positive voltages to the grids. idle current was measured across 1 ohm resistors in the anodes. Using roughly 5 volts DC (variable) fed to the grids through a high value resistance on the individual grids I could get them to balance. A second amp I used the 32s in push-pull U/L parallel with two tubes per channel with the individual sections in each tube tied together. Balance was then by the 25 ohm pot I use in nearly all similar amps. In neither amp did I get as much output as I hoped for. I don't recall the values right now, but it seemed to be about 5-6 watts in the one and about 10 in the other. The sound quality of the amps was not up to what I would consider hi-fi standards. Since these are RF tubes, I suspect that the response was non-linear in the power range I desired and was causing a lot of harmonic distortion. Since both amps were significantly below the performance level I felt minimal I discarded the project.

For a general purpose amp they may be suitable. The tubes do look cool though. A pair of EL84s will run circles around them for audio though and you don't need to find the anode clips or funky sockets.

Can you share a schematic for the 6P3C? I have some left from my Priboj amp and even though the tube isn't the most reliable tube, it's still awsome to be able to do something with this dual power tetrode.

However, the 829 is said to be very much like a dual 6L6 so you could either start with a schematic for 6L6, with the halves either separately - one half for each channel - or parallelled.I will finish an 832-SE when we get home from the States. I am using a single 832 (using 6V6 schematics) and, as there's only a single cathode connection for both halves, I have halved the R and doubled the C. As driver a 6SL7, resulting in a two-tube amp.

_________________Magnus

“If you don't know where you are going, any road will get you there.”―Lewis Carroll

g2 bypass? Seen this arrangement a few times. The one that comes to mind is the Fender Champ 5F1. Drawn a little different, but it's the same arrangement. I was just being silly about a g2 bypass, however, given its value....... Otherwise, it's just a small filter.

_________________The key to a successful build is to keep the smoke IN the circuit. -Les

I make one little suggestion.... Some clear heat shrink on the anode connections - for safety's sake. Sorry, jus the way I am. I don't like exposed lethal voltage terminals..Otherwise, very cool looking. Almost "sci-fi"ish -- imagine perspective shooting: tube looks 50' tall with average height humans standing in awe of the tube's glorious power..

_________________The key to a successful build is to keep the smoke IN the circuit. -Les

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